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Author Topic: pH Meter Calibration  (Read 5146 times)

Offline johnnyb

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Re: pH Meter Calibration
« Reply #15 on: June 30, 2015, 04:49:57 pm »
My pH56 takes a while to get a reading too. I have a little laboratory arm to hold it. I cool the wort to under 80 in a small 40ml beaker, stick the meter probe in it, lock it in place with the arm, and go do something else for 10 minutes or so.

It doesn't take long to calibrate though. I can do that holding it in the solution. It locks in on the calibration solution way faster than on something like wort.


Offline metron-brewer

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Re: pH Meter Calibration
« Reply #16 on: June 30, 2015, 05:15:48 pm »
I've had the same slow read time issues from the day I bought it. The fact that I could replace the probe was a big selling point to me. After having some experience using a meter and this one in particular, I'll definitely be looking at some other models when/if I ever have to replace it.
Ron B.
White Bear Lake, MN

Offline pfabsits

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Re: pH Meter Calibration
« Reply #17 on: July 01, 2015, 03:09:07 pm »
I've had the same slow read time issues from the day I bought it. The fact that I could replace the probe was a big selling point to me. After having some experience using a meter and this one in particular, I'll definitely be looking at some other models when/if I ever have to replace it.

How fast a pH reading stabilizes is affected by a variety of factors. They include:
1) Probe properly hydrated
2) Is the probe clean
3) The type of junction used
4) Is the junction clogged
5) The conductivity of the solution
6) Age of the probe

If a probe is not hydrated then as the probe sits in a solution a thin hydrated layer will form on the glass. This change will affect the electrode characteristic causing the the calibration not to be valid. Overall there will be a very very slight drift in readings. For this reason it is important to store in a solution. Whether storage (ideal), 3.5M KCl adjusted to pH 4, or buffer solution all will help to maintain the hydration layer that takes about 3-4 hours to fully form.

Even though hydration can be an issue, a coating on the probe would more likely be a source of drifting than the lack of the hydration layer. Every pH probe has two wires. One is inside the indicating glass electrode and the other in the reference. If a coating is on the glass it will impede the circuit causing stability issues.

The other are of concern would be the junction. There are many different types of junctions including those made of ceramic, cloth, Teflon, glass, and open. If the junction gets clogged the circuit is impeded and erratic readings will be seen. The Milwaukee pH-56 has cloth junction. it is about 1/8 to 1/4" wide and about 1-2" in length. If you look at the bottom of the probe you will see what looks like a small piece of paper sticking out. It can be seen on the link to the Milwaukee site and the Hanna site below. The junction of the pH-56 is extractable. When erratic readings are observed simply pull about 1/8" of the junction out. This will clear any clogging and the response time should change dramatically.

All pH electrodes need a solution that is conductive to work. Typically at least 100 uS/cm. Mash and Wort should be well above this so it should not be an issue. 100 uS/cm is pretty low. For example, if I remember right, Lake Michigan is about 300 uS/cm. Reverse Osmosis water is 30-40 uS/cm.

All pH electrodes age. The glass does breakdown. A probe should last at least 1-2 years. One of the things that cause probes to fail prematurely is using at high temps. We typically say at 25 oC (ambient) a probe will last 1-2 years. Every 25 oC increase cuts that in half. So at 50 oC a probe will last 6-12months, at 75 oC 3-6 months and at 100 oC about a month. As the resistance of the glass changes so does the impedance of the circuit.

There different glass types including those that are made for taking temperatures at higher temperatures. As it was pointed out earlier there is the argument whether the pH value at one temperature is the same at a different temperature. The ATC of any pH meter is correcting for the change of the resistance of the glass with temperature. It does not compensate for the actual effect of temperature on any particular solution. Considering that unless you know that you have a good offset/slope the actual reading obtained with any meter is going to be less accurate than the affect of temperature on the solution. I have seen 0.5 to 1 pH discrepancies. I usually see this when a probe is being used well outside a good operating spec of +/- 25 mV in pH 7 and a slope greater than 90%.

http://www.milwaukeetesters.com/pdf/product-specs/pH55-56.pdf

http://shop.hannainst.com/hi98107-phep-ph-tester.html

One of the avid home brewers that work for Hanna Instruments

Offline johnnyb

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Re: pH Meter Calibration
« Reply #18 on: July 01, 2015, 03:19:37 pm »
When you pull out the junction, do you trim off the old section?

Offline pfabsits

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Re: pH Meter Calibration
« Reply #19 on: July 02, 2015, 07:02:50 am »
Since it is recessed from the plastic edge, I would not cut off the first time. But once it passes the edge of the plastic body then I would trim. Just be careful when you pull out. It does not take much force to make it move. I usually use a small screwdriver and press up against the side of the meter. Just be careful that you do not lean the screwdriver back into the glass probe and use as a fulcrum. You will break the glass. If you accidentally pull it all the way out (1-2" long) then with a small screwdriver it can be pushed back in.

Without having the Milwaukee meter here in front of me it is hard to say but there should be a rubber/silicone gasket that holds the junction and electrode in place.
One of the avid home brewers that work for Hanna Instruments

Offline metron-brewer

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Re: pH Meter Calibration
« Reply #20 on: July 02, 2015, 07:09:18 am »
I looked at my meter last night and did not see the junction sticking out. It is a replacement probe tip so maybe they don't have that option?
Ron B.
White Bear Lake, MN

Offline johnnyb

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Re: pH Meter Calibration
« Reply #21 on: July 02, 2015, 11:49:26 am »
I looked at my meter last night and did not see the junction sticking out. It is a replacement probe tip so maybe they don't have that option?

I just checked mine too (pH56) and I don't have a visible junction either. This is the original probe, and it's about 4 years old but still works fine. (Was unused but stored properly in the storage solution for several years.)

Edit: I'm a dumb ass. Looked at the picture then got my reading glasses out and low and behold it does have a visible junction. Or should I say it DID have a junction. I pulled it down a little with a tiny screwdriver. It barely went beyond the end of the probe. I went to trim it with scissors and the whole thing yanked out. I cannot get it back in lolz.

« Last Edit: July 02, 2015, 12:07:31 pm by johnnyb »

Offline pfabsits

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Re: pH Meter Calibration
« Reply #22 on: July 02, 2015, 01:22:07 pm »
I looked at my meter last night and did not see the junction sticking out. It is a replacement probe tip so maybe they don't have that option?

I just checked mine too (pH56) and I don't have a visible junction either. This is the original probe, and it's about 4 years old but still works fine. (Was unused but stored properly in the storage solution for several years.)

Edit: I'm a dumb ass. Looked at the picture then got my reading glasses out and low and behold it does have a visible junction. Or should I say it DID have a junction. I pulled it down a little with a tiny screwdriver. It barely went beyond the end of the probe. I went to trim it with scissors and the whole thing yanked out. I cannot get it back in lolz.

Attached is a picture of the junction taken out of the Hanna HI73217 probe. The junction is actually 1" long.

I was able to get the junction back into the electrode after taking a picture. Do the reverse. Place the junction against the side and use the screwdriver to to push back into the black rubber ring.

Only a very small portion should be extracted 1/8" or less. Just enough to clear any clogging and only should be done when the readings are erratic or taking a very long time to stabilize.

I am pretty sure that the Milwaukee junction is the same length. But just in case, do so at your own risk. I am sorry Johnnyb. Message me outside the forum if you cannot get back in or if you do and the meter does not work.




« Last Edit: July 02, 2015, 01:24:27 pm by pfabsits »
One of the avid home brewers that work for Hanna Instruments

Offline johnnyb

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Re: pH Meter Calibration
« Reply #23 on: July 02, 2015, 01:34:27 pm »
No need to apologize -- it was my own fault! You did say to be very careful. The end of my junction was filthy which was why I decided to pull it out a bit.

My probe is 4 years old anyway, so I'm just going to order a new one. No worries.

And now I'm a little wiser to the whole pH meter thing!